全文获取类型
收费全文 | 400721篇 |
免费 | 4243篇 |
国内免费 | 1251篇 |
专业分类
化学 | 211396篇 |
晶体学 | 6897篇 |
力学 | 17687篇 |
综合类 | 12篇 |
数学 | 42924篇 |
物理学 | 127299篇 |
出版年
2020年 | 3253篇 |
2019年 | 3686篇 |
2018年 | 4578篇 |
2017年 | 4569篇 |
2016年 | 6829篇 |
2015年 | 4250篇 |
2014年 | 6916篇 |
2013年 | 17696篇 |
2012年 | 12950篇 |
2011年 | 15956篇 |
2010年 | 11317篇 |
2009年 | 11291篇 |
2008年 | 14574篇 |
2007年 | 14450篇 |
2006年 | 13626篇 |
2005年 | 12353篇 |
2004年 | 11324篇 |
2003年 | 10228篇 |
2002年 | 10001篇 |
2001年 | 12008篇 |
2000年 | 9171篇 |
1999年 | 7134篇 |
1998年 | 5816篇 |
1997年 | 5716篇 |
1996年 | 5472篇 |
1995年 | 5036篇 |
1994年 | 4897篇 |
1993年 | 4821篇 |
1992年 | 5528篇 |
1991年 | 5560篇 |
1990年 | 5312篇 |
1989年 | 5266篇 |
1988年 | 5323篇 |
1987年 | 5229篇 |
1986年 | 4950篇 |
1985年 | 6581篇 |
1984年 | 6782篇 |
1983年 | 5369篇 |
1982年 | 5637篇 |
1981年 | 5605篇 |
1980年 | 5312篇 |
1979年 | 5742篇 |
1978年 | 5816篇 |
1977年 | 5878篇 |
1976年 | 5764篇 |
1975年 | 5261篇 |
1974年 | 5285篇 |
1973年 | 5260篇 |
1972年 | 3679篇 |
1968年 | 3114篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
71.
72.
73.
74.
75.
Pan Huang Dawen Xu Robert M. Reich Felix Kaiser Boping Liu Fritz E. Kühn 《Tetrahedron letters》2019,60(24):1574-1577
A first example of an Et2Zn mediated silylation of 1-aklynes is reported. A series of functional groups are tolerated in this reaction. Mechanistic studies support Zn alkynilides as intermediates in the reaction. This reaction protocol provides a practical method for the preparation of alkynylsilanes and expands the application of organometallic zinc in organic synthesis. 相似文献
76.
Vanessa R. Machado Louis P. Sandjo Giovanni L. Pinheiro Milene H. Moraes Mario Steindel Moacir G. Pizzolatti 《Natural product research》2018,32(3):275-281
The natural product lupeol 1 was isolated from aerial parts of Vernonia scorpioides with satisfactory yield, which made it viable to be used as starting material in semisynthetic approach. Ten lupeol derivatives 2–11 were prepared by classical procedures. Including, five new esters derivatives 7–11, which were obtained by structural modifications in the isopropylidene fragment. All semisynthetic compounds and lupeol 1–11 were confirmed by 1H NMR, 13C NMR and HRMS. Their antiprotozoal activity was evaluated in vitro against L. amazonensis and T. cruzi. Derivative 6 showed the best antitrypanosomal activity (IC50 = 12.48 μg/mL) and the lowest cytotoxic derivative (CC50 = 161.50 μg/mL). The mechanism of action of the most active derivatives (4, 6 and 11) is not dependent from the enzyme trypanothione reductase. 相似文献
77.
N. I. Golovina G. N. Nechiporenko G. G. Nemtsev G. P. Dolganova V. P. Roshchupkin D. B. Lempert G. B. Manelis 《Russian Journal of Applied Chemistry》2007,80(1):24-30
Methods for phase stabilization of ammonium nitrate were sought for in order to considerably expand the application area of this oxidizing agent in various-purpose self-combustible formulations, including that in a new generation of gas-generating formulations for automobile air bags. New methods for stabilization of ammonium nitrate were studied and, in particular, a search was made for organic compounds that can stabilize ammonium nitrate even at their low content. The mechanism of phase state stabilization of ammonium nitrate by compounds of this kind was examined. 相似文献
78.
79.
A combination of 1,3-dihalo-5,5-dimethylhydantoin (X = Br, Cl) and sodium nitrite in the presence of wet SiO2 was used as an effective nitrosating agent for the nitrosation of N,N-dialkyl amines to their corresponding nitroso derivatives under mild and heterogeneous conditions in good to excellent yields. 相似文献
80.
An attempt is made to find out the suitable entrainment and exit boundary conditions in laminar flow situations. Streamfunction vorticity formulation of the Navier–Stokes equations are solved by ADI method. Two‐dimensional laminar plane wall jet flow is used to test different forms of the boundary conditions. Results are compared with the experimental and similarity solution and the proper boundary condition is suggested. The Kind 1 boundary condition is recommended. It consists of zero first derivative condition for velocity variable and for streamfunction equation, mixed derivative at the entrainment and exit boundaries. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献